Eating a diet high in methionine, an amino acid found in meat, fish, dairy, and egg products, may increase the risk of memory loss, according to findings recently presented at the Experimental Biology Annual Meeting in Boston.
The study builds on previous knowledge of excess methylation and the role it may play in memory loss by silencing genes that contribute to cognitive function. The researchers speculated that a diet high in methionine may increase methylation of netrins, a protein involved in brain maintenance, resulting in memory loss.
Anuradha Kalani, of the University of Louisville, and colleagues fed mice a diet high in methionine (1.2%), and low in folate (0.08 mg/kg), vitamin B6 (0.01 mg/kg), and B12 (10.4 mg/kg) for six weeks. Memory function in the mice and the control group was monitored via a test that measured their response to a fear stimulant.
Compared to the control group, mice fed the methionine diet stopped responding to the fear stimulant that had previously induced fear after four weeks, suggesting a loss of memory. The longer the mice were on the diet, the less netrin was expressed and more methylation occurred. To isolate whether or not this result was from silencing of the netrin gene, researchers injected the brains of the mice with netrin genes. The injection restored the long-term memory in the mice by about 50%, confirming that an increase in methionine induced hypermethylation of netrin, silencing the gene and causing memory loss. Additionally, researchers found that mice eating the high methionine diet had reduced levels of DCC, a netrin receptor.
“Our findings suggest that an excess methionine diet caused memory impairment and hyper-methylation that affected netrin expression, which is a protein important in maintaining synaptic plasticity and involved in axonal guidance and neurogenesis,” the researchers wrote.